导数公式的证明最全版.docx
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导数公式的证明最全版
导数的定义:
f'(x)=limAy/Ax
△x宀0(下面就不再标明Axt了)
用定义求导数公式
(1)f(x)=xAn
证法一:
(n为自然数)
f(x)
=lim[(x+A-xAn]/Ax
=lim(x+-A)[(x+Ax)A(n+x*(x+Ax)A2)+…+xA(n-2)*(x+Ax)+xA1)j/Ax
=lim[(x+Ax)/-(t)+x*(x+Ax)A2)+...+xA(n-2)*(x+Ax)+x-in]
=xA(n-1)+x*xA(n-2)+xA2*xA(n-3)+…xA(n-2)*x+xA(n-1)
=nxA(n-1)
证法二:
(n为任意实数)
f(x)=xAn
lnf(x)=nlnx
(lnf(x))'=(nlnx)'
f(x)/f(x)二n/x
f(x)=n/x*f(x)
f(x)=n/x*xAn
f(x)=nxA(n-1)
(2)f(x)=sinx
f(x)
=lim(sin(x+-sinX)/Ax
=lim(sinxcosAx+cosxsinx)/AxXx
=lim(sinx+cosxsin-sinx)/xAx
=limcosxsinAx/Ax
=cosx
(3)f(x)=cosx
f(x)
=lim(cos(x+-ctosx)/Ax
=lim(cosxcos-sinxsin-Acxx)/Ax
=lim(cosx-sinxsin-Aos)/Ax
=lim-sinxsinAx/Ax
=-sinx
(4)f(x)=aAx
证法一:
f(x)
=lim(aA(x+-aAx)/Ax
=limaAx*(aA-1)/xAx
(设aAA-1=m,贝卩Ax=logaA(m+⑪
=limaAx*m/logaA(m+1)
=limaAx*m/[ln(m+1)/lna]
=limaAx*Ina*m/ln(m+1)
=limaAx*lna/[(1/m)*ln(m+1)]
=limaAx*lna/ln[(m+1)A(1/m)]
=limaAx*Ina/lne
=aAx*Ina
证法二:
f(x)=aAx
Inf(x)=xIna
[lnf(x)]'=[xlna]'
f(x)/f(x)=lna
f(x)=f(x)Ina
f(x)=aAxIna
若a=e,原函数f(x)=eAx
则f'(x)二eAx*Ine=eAx
(5)f(x)=IogaAx
f(x)
=lim(IogaA(x+-logxAx)/Ax
=limIogaA[(x+Ax)/x]/Ax
=limIogaA(1+Ax/x)/Ax
=limIn(1+Ax/x)/(lna*Ax)
=limx*ln(1+Ax/x)/(x*Ina*Ax)
=lim(x/Ax)*ln(1+Ax/x)/(x*lna)
=limIn[(1+△x/x)八(x/△x)]/(x*Ina)
=limIne/(x*Ina)
=1/(x*Ina)
若a=e,原函数f(x)=IogeAx=Inx
贝卩f'(x)=1/(x*Ine)=1/x
(6)f(x)=tanx
f(x)
=Iim(tan(x+-△nx)/△x
=Iim(sin(x+△x)/cos(x+nx/ob^)/△x
=Iim(sin(x+△x)Coxcos(k+△x)/(△xcosxcos(x+△x))
=Iim(sinxcos△xcosx+sin△xcosxcosx
sinxcosxcos△x+sinxsinxsin△x)/(△xcosxcos(x+△x))
=Iimsin△x/(△xcosxcos(x+△x))
=1/(cosxF2二secx/cosx=(secx)A2=1+(tanx)A2
(7)f(x)=cotx
f(x)
=Iim(cot(x+-cMx)/△x
=Iim(cos(x+△x)/sin(x+-cos2x/x)nx)/△x
=Iim(cos(x+
=Iim(cosxcos
cosxsin△xcosx)/(
△xjsinxsin(x+△x))/(△xsinxsin(x+△x))
△-sSnsinxsin-cosxsinxcos-△x
△xsinxsin(x+△x))
=Iim-sin△x/(△xsinxsin(x+△x))
=-1/(sinx)八2二-cscx/sinx=-(secx)八2=-1-(cotx)八2
(8)f(x)=secx
f(x)
=lim(sec(x+Asx)dx)/Ax
=lim(1/cos(x+-t/cx$x)/Ax
=lim(cosx-cos(x+Ax)/(AxcosxcosAx)
=lim(cosx-cosxcosAx+sinxsinAx)/(Axcosxcos(x+Ax))
=limsinxsinAx/(Axcosxcos(x+Ax))
二sinx/(cosx)A2=tanx*secx
(9)f(x)=cscx
f(x)
=lim(csc(x+Adxcx)/Ax
=lim(1/sin(x+-A/x)nx)/Ax
=lim(sinx-sin(x+Ax))/(Axsinxsin(x+Ax))
=lim(sinx-sinxcosAixAxcosx)/(Axsinxsin(x+Ax))
=lim-sinAxcosx/(Axsinxsin(x+Ax))
=-cosx/(sinx)A2二-cotx*cscx
(10)f(x)=xAx
Inf(x)=xInx
(Inf(x))'=(xlnx)'
f(x)/f(x)=lnx+1
f(x)=(lnx+1)*f(x)
f(x)=(lnx+1)*x^x
(12)h(x)=f(x)g(x)
h'(x)
=lim(f(x+△x)g(fx)g(x))/Ax
=lim[(f(x+-f(A)x)f(x))*g(x+Ax)+(ggx+-g(x+xAx))*f(x)]/Ax
=lim[(f(x+-f(A)x*g(x+Ax)+(g(xJ(x)Af(x)+f(x)*g(x+-f(x)*g(x+Ax)]/Ax
=lim(f(x+Afxx))*g(x+Ax)/Ax+-g(x)^*f(A))t)Ax
=f(x)g(x)+f(x)g'(x)
(13)h(x)=f(x)/g(x)
h'(x)
=lim(f(x+Ax)/g(xf(x)g(xx)/Ax
=lim(f(x+Ax)6=lim[(f(x+-f(A)x)f(x))*g(x)-(g(x+Ag(x)+g(x))*f(x)]/(Axg(x)g(x+Ax))
=lim[(f(x+Afx)))*g(x)-(g(x+Ag(x))*f(x)+f(x)g(x)-f(x)g(x)]/(Axg(x)g(x+Ax))
=lim(f(x+-Axx)*g(x)/(Axg(x)g-(g(x+AA(g(x))*f(x)/(Axg(x)g(x+Ax))
=f(x)g(x)/(g(x)*g(x))-f(x)g'(x)/(g(x)*g(x))
=[f(x)g(x)-f(x)g'(x)]/(g(x)*g(x))x
(14)h(x)=f(g(x))
h'(x)
=lim[f(g(x+-f(gxx))]/Ax
=lim[f(g(x+-g(k)+g(x))f(g(x))]/Ax
(另g(x)二u,g(x+Ax)(x)二A)
=lim(f(u+-Au))/Ax
=lim(f(u+-Au))*Au/(Ax*Au)
=limf(u)*Au/Ax
=limf(u)*(g(x+-g(x))/x)Ax
=f(u)*g'(x)=f,(g(x))g'(x)
(反三角函数的导数与三角函数的导数的乘积为1,因为函数与反函数关于y=x对称,所以导数也关于y=x对称,所以导数的乘积为1)
(15)y=f(x)二arcsinx
贝卩siny=x
(siny)'=cosy
所以
(arcsinx)'=1/(siny)'=1/cosy
=1/“1inyF2
(siny=x)
=1/V-kA2
即f'(x)=1/“1
(16)y=f(x)=arctanx
贝卩tany=x
(tany)'=1+(tanyF2=1+xA2
所以
(arctanx)'=1/1+xT
即f'(x)二1/1+xA2
总结一下
(xAn)'二nxA(n-1)
(sinx)'二cosx
(cosx)'=-sinx
(aAx)'=aAxIna
(eAx)'=eAx
(logaAx)'=1/(x1na)
(Inx)'=1/x
(tanx)'=(secx)A2=1+(tanx)A2
(cotx)'=-(cscx)A2=-1-(cotx)A2
(secx)'=tanx*secx
(cscx)'=-cotx*cscx
(xAx)'=(Inx+1)*xAx
(arcsinx)'=1/-x91
(arctanx)'=1/1+xA2
[f(x)g(x)]'=f(x)g(x)+f(x)g'(x)
[f(x)/g(x)]'=[f(x)g(x)-f(x)g'(x)]/(g(x)*g(x))
[f(g(x))]'=f'(g(x))g'(x)